Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:                ACID HARQ channel identifier        ACK acknowledgment        BS base station        CID connection identifier        CRC cyclic redundancy check        DL downlink (e.g., BS towards MS)        HARQ hybrid automatic repeat request        IE information element        LTE long term evolution        MAC medium access control        MCS modulation coding scheme        MS mobile station        N_ACID number of asynchronous channels        OFDM orthogonal frequency division multiplex        OFDMA orthogonal frequency division multiple access        PDU protocol data unit        PHY physical        QAM quadrature amplitude modulation        QPSK quadrature phase shift keying        UL uplink (e.g., MS towards BS)        VoIP voice over internet protocol        
This section is intended to provide a background or context to this invention. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Recently the IEEE 802.16 working group has established a new task group, 802.16m, to provide an advanced air interface which amends IEEE 802.16-2004 (see IEEE 802.16-2004, “IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems,” Jun. 24, 2004) and 802.16e (see IEEE 802.16e-2005, “IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems,” Feb. 28, 2006) in order to meet the requirements of next generation mobile networks. One target of the 802.16m specification work is to improve the VoIP capacity of the system (see in general Draft IEEE 802.16m Requirements, 2007-10-19).
The VoIP support in the current IEEE 802.16 specification is not efficient due at least to the bandwidth consumption by the DL-MAP and UL-MAP messages, and the generic MAC header found in every frame that transmits the VoIP packets.
After a VoIP session is activated, VoIP packets typically arrive at the MAC layer from an upper layer periodically both for the downlink and the uplink. The VoIP packet size can remain the same for some tens of frames and then change to another state. As a result, the bandwidth (PHY resources) in a number of future frames that is needed for the transmission of VoIP packets is nearly predetermined. However, in the current IEEE 802.16 standard definition the bandwidth allocation information (MAP-IE) is broadcast to the SS, also referred to herein as a MS, in every frame using DL-MAP, UL-MAP messages, as shown in FIG. 1. That is, the bandwidth is allocated to the MS in a per-frame manner.
While this type of bandwidth allocation method is dynamic, the signaling overhead can be too great when running a VoIP application. For example, the DL-MAP-IE and the UL-MAP-IE are 7.5 bytes and 4 bytes, respectively. Note as well that the use of a repetition code is typically needed for the transmission of the DL-MAP and the UL-MAP. Therefore, the bandwidth consumption of this signaling overhead in DL-MAP and UL-MAP can be excessive.
In addition to the MAP messages, for both the downlink and the uplink, the 6-byte generic MAC header presents additional signaling overhead. FIG. 2 shows the MAC PDU structure of an exemplary VoIP codec, the widely used AMR 12.2k. A MAC-layer ARQ is not needed for VoIP, so the CRC is not needed in the MAC PDU. The voice source encoder outputs a 31-byte packet every 20 ms. The IP/UDP/RTP header is normally compressed to 4 bytes. Thus, the payload of this MAC packet is 35 bytes.
Assuming a case that a repetition coding of 4 is used for the MAP messages, and the MCS of PHY burst for VoIP is QPSK/rate-0.5 coding (the same with MAP messages), and taking the uplink as an example, the signaling overhead of an uplink VoIP packet isUL-MAP-IE+generic MAC header=4(bytes)*8(bits)/1(bit/s/Hz)*4(repetition code)+6(bytes)*8(bits)/1(bit/s/Hz)=176(data subcarriers),which is too large for the payload:35(bytes)*8(bits)/1(bit/s/Hz)=280(data subcarriers).
Note that when the MCS of the PHY burst containing the VoIP packet is more efficient than the MCS for the MAP messages, which is typically the case, the signaling overhead is even larger as compared to the payload.
Of interest to the ensuing description of the exemplary embodiments of this invention is the persistent scheduling approach in 3GPP-LTE (e.g., see 3GPP RAN1 R1-063275, “Discussion on control signaling for persistent scheduling of VoIP”, Samsung), as well as the scheduling method presented in section 6.3.6.7.3 of IEEE 80216j-06—026r4, “IEEE 802.16j Baseline Document”.